package jrummikub.ai.fdsolver.constraint;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;

import jrummikub.ai.fdsolver.Constraint;
import jrummikub.ai.fdsolver.Propagator;
import jrummikub.ai.fdsolver.Satisfiability;
import jrummikub.ai.fdsolver.Var;

public class IndexConstraint<T> implements Constraint {
	Var<T> target;
	Var<Integer> index;
	List<Var<T>> list;
	Collection<Var<?>> vars = new ArrayList<Var<?>>();
	Collection<Var<?>> varsNoTarget = new ArrayList<Var<?>>();
	Collection<Var<?>> varsNoIndex = new ArrayList<Var<?>>();

	public IndexConstraint(Var<T> target, Var<Integer> index, List<Var<T>> list) {
		this.target = target;
		this.index = index;
		this.list = list;
		vars.addAll(list);
		vars.add(index);
		vars.add(target);
		varsNoTarget.addAll(list);
		varsNoTarget.add(index);
		varsNoIndex.addAll(list);
		varsNoIndex.add(target);
	}

	@Override
	public Collection<Var<?>> getWatchedVars() {
		return vars;
	}

	private class UnionProp implements Propagator {
		@Override
		public Collection<Var<?>> getWatchedVars() {
			return varsNoTarget;
		}

		@Override
		public void propagate() {
			HashSet<T> union = new HashSet<T>();
			for (int i : index.getRange()) {
				union.addAll(list.get(i).getRange());
			}
			for (Iterator<T> i = target.iterator(); i.hasNext();) {
				T val = i.next();
				if (!union.contains(val)) {
					i.remove();
				}
			}
		};
	}

	private class IndexProp implements Propagator {
		@Override
		public Collection<Var<?>> getWatchedVars() {
			return varsNoIndex;
		}

		@Override
		public void propagate() {
			for (Iterator<Integer> i = index.iterator(); i.hasNext();) {
				int id = i.next();
				HashSet<T> range = new HashSet<T>(target.getRange());
				range.retainAll(list.get(id).getRange());
				if (range.isEmpty()) {
					i.remove();
				}
			}
		}
	}

	private class VarProp implements Propagator {
		@Override
		public Collection<Var<?>> getWatchedVars() {
			return Arrays.asList(target, index);
		}

		@Override
		public void propagate() {
			if (index.getRange().size() != 1)
				return;
			int id = index.getValue();
			Var<T> var = list.get(id);
			for(Iterator<T> i = var.iterator(); i.hasNext();) {
				if (!target.getRange().contains(i.next())) {
					i.remove();
				}
			}
		}

	}

	@Override
	public Collection<Propagator> getPropagators(boolean negate) {
		if (negate) {
			return Collections.emptyList();
		}
		return Arrays.<Propagator> asList(new UnionProp(), new IndexProp(), new VarProp());
	}

	@Override
	public Satisfiability getSatisfiability() {
		HashSet<T> union = new HashSet<T>();
		for (int i : index.getRange()) {
			union.addAll(list.get(i).getRange());
		}
		boolean isSat = false;
		for (T val : target.getRange()) {
			if (union.contains(val)) {
				isSat = true;
				break;
			}
		}
		if (!isSat) {
			return Satisfiability.UNSAT;
		} else {
			if (union.size() == 1 && target.getRange().size() == 1) {
				return Satisfiability.TAUT;
			} else {
				return Satisfiability.SAT;
			}
		}
	}
}